1. Field of the Invention
This invention relates to a method for making a definitive prosthesis socket for fitting residual limbs to prostheses.
2. Background of the Prior Art
Definitive sockets for fitting prostheses to residual limbs of amputees are made by various processes in accordance with prior art techniques, including molding thermosetting, thermoforming or other known resinous materials to obtain a final rigid socket shape that will receive a residual limb and structurally react loads between the prosthesis and the residual limb without discomfort to the user. Such molded sockets without and with reinforcements are exemplified in U.S. Pat. Nos. 5,163,965, granted Nov. 17, 1992 to Rasmusson and Fischl; and 5,263,990, granted Nov. 23, 1993 to Handal, respectively.
In accordance with a well known technique for molding definitive sockets of resinous materials, a male or positive mold of the residual limb area is made from a plaster of paris female or negative casting sleeve that has been formed by molding the sleeve directly against the residual limb, sometimes with the aid of a known pressure casting system of the type exemplified by the ICECAST(trademark) system made of xc3x96ssur h.f. of Reykjavik, Iceland. The positive mold is then adjusted or xe2x80x9crectifiedxe2x80x9d in accordance with well known techniques to provide relief for sensitive areas of the residual limb and to obtain a correctly sized socket that will properly fit the residual limb. The multiple step molding and rectification process is well known and has been extensively described in literature and texts known to prosthetists. The process is time-consuming expensive and heavily dependent on the individual skills of the prosthetist.
Other procedures for molding interim or definitive sockets have been described in the prior art, including a procedure whereby SCOTCHCAST(copyright) tape made by 3M Company of Minneapolis, Minn., has been utilized to produce an interim prosthesis socket for below-knee amputees. The SCOTCHCAST(copyright) tape was wrapped directly over the residual limb after a tube sock was applied to the residual limb and manual compressive pressure was applied to the SCOTCHCAST(copyright) tape while it was curing to a hardened condition to provide relief for the patellar tendon area to form a PTB bar and to control the anterior-posterior diameter for weight bearing. (Wu et al., xe2x80x9cSCOTCHCAST(copyright) P.V.C. Interim Prosthesis for Below-Knee Amputeesxe2x80x9d, Bulletin of Prosthetics Research 10-36, Fall 1981, pp. 40-45). This process, however, has not been reported as being suitable for forming definitive prosthesis sockets suitable for continuous long-term use.
The present invention is concerned with a molded residual limb definitive prosthesis socket formed by using a single step pressure casting technique that enables the production of the socket with an internal form that is substantially in finished condition upon completion of the casting process. The socket is molded directly on a residual limb using a reinforced resinous material that in a preferred form of the invention is pre-formed as a pre-impregnated (xe2x80x9cpre-pregxe2x80x9d) tubular mat or web of reinforcing strands or elements impregnated with a hardenable uncured or unhardened moldable preferably resinous material that is assembled with a suitable prosthesis coupler that is ultimately unified with the molding material during molding and curing of the socket. Suitable liner and covering fabric layers may be bonded to the inner and outer surfaces of the socket material during molding and pressure relieving resilient material may be incorporated in the socket during molding as well.
The molding of the socket is carried out using a compressive pressure casting technique modified so that tension is applied to the distal end of the residual limb in the distal direction during hardening of the socket material. In a preferred embodiment of the invention, the tension is applied through a resilient, impermeable suction socket or sleeve that has been placed on the residual limb between the limb and the socket material. It has been discovered that the application of such tension to the residual limb distally distends the soft tissue of the residual limb relative to the underlying skeletal bone(s) and reduces it in size diametrically. The application of such tension during pressure casting of the socket material produces a virtually final or definitive desired fit between the residual limb and the socket. Thus, the invention reflects the discovery that the combination of tension applied to the distal end area of the residual limb and compression casting of the socket material directly on the residual limb while under such tension enables a prosthetist to mold a definitive socket for prosthetic use in a single step using a moldable and hardenable socket material that possesses the necessary load bearing structural characteristics for a prosthesis socket.
A preferred moldable curable socket material in accordance with this invention comprises a tubular mat of braided carbon fiber reinforcing strands impregnated with a water curable polyisocyanate type prepolymer. The exemplary socket pre-form assembly includes a prosthesis coupler element integrated into one end of the socket assembly before molding and hardening.